fix(p2p): validate chain exchange responses for block headers

[hanabi1224]

Summary of changes

Part of #4441 investigation

Confirmed that ChainExchange failures should be in the console output or log. Theoretically, there is a chance that a remote peer always returns a successful empty response and leads the downloading code to a dead loop with no errors.

This PR tries to mitigate the issue by adding validation logic to the chain exchange response

Changes introduced in this pull request:

• add validation logic to the chain exchange response
• minor logging improvement
• use NonEmptyU64 instead of u64 for chain_exchange request_len
• refine stateless peer filtering logic to fallback to all peers when the result is empty

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• [x] I have performed a self-review of my own code,
• [x] I have made corresponding changes to the documentation,
• [x] I have added tests that prove my fix is effective or that my feature works (if possible),
• [x] I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

[hanabi1224]

I'm still waiting for a unit test but manage my expectations. No bonusly to incentivize one. :(

@LesnyRumcajs unit tests added!